This invention relates to flow control means and more particularly to means and a method for reducing pressure in the flow of a shear-sensitive liquid.
Shear-sensitive liquids include various polymer solutions, carboxymethyl-cellulose, hydroxyethyl-cellulose, latex polymers, polysaccharides, and the like. Important examples of shear-sensitive liquids are liquid polymer solutions used in oil recovery flooding operations such as polyacrylamide solutions. In flooding techniques, liquid is injected into a formation to displace oil therefrom. A large body of prior art has developed in the use of various liquids under selected conditions. Many different types of water solutions including cosurfactants have been used. Flooding with polymer solutions has gained popularity in use since it can provide the ability to sweep greater fractions of reservoir volume in comparison to conventional waterfloods.
One of the most important characteristics of polymer solutions is their viscosity. Due to their molecular structure, viscous polymer solutions are subject to mechanical degradation when subjected to shear forces. In use, however, the potential for application of such forces is continually present.
In flooding operations, a large amount of polymer solution must be provided from one source, such as a mixing tank, to several wellheads some of which will usually be remote from the polymer supply source. The polymer solutions are pumped to wellheads by one or more large positive displacement pumps. Typical supply pressures may be as high as 2500 psig. However, the discharge pressure into the wellhead is a function of the well characteristics and the geology of the formation. The well could represent a very low resistance to flow, and therefore require a low pressure input. It is necessary to provide a means of flow control to reduce the pressure from the high pressure polymer source to the low pressure well. Mere use of a pressure reduction valve would result in turbulence and the creation of shear forces which would reduce the viscosity of the liquid polymer. A throttle valve, for example, can cause serious degradation in terms of decrease in viscosity. Various solutions to the problem of providing shear-sensitive liquids from a high pressure source to a low pressure input have been used, but all prior devices and methods have various drawbacks.
A highly satisfactory solution has been disclosed in commonly assigned applications Ser. No. 322,729 filed by Peter L. Sigwardt on Nov. 19, 1981. The apparatus of that application provies a flow rate controller for an input supply of relatively high pressure controlled liquid and the discharge therefrom of controlled liquid at a reduced pressure relative to the pressure of the input supply of controlled liquid. The flow rate controller of Application Ser. No. 322,729 provides means for directing the input portion of high pressure controlled liquid into contact with a first movable barrier in a high pressure displacement chamber to impose through said first barrier a relatively high pressure upon a substantially confined portion of control liquid on the opposite side of the first barrier. The high pressure control liquid is conveyed through a control conduit having a flow control means therein into a reduced pressure displacement chamber, and means for transmitting pressure of the reduced pressure control liquid through a second movable barrier to displace from the reduced pressure chamber a portion of the controlled liquid at a lower pressure than the pressure of the input controlled liquid.
In the operation of this apparatus, control liquid is introduced alternately against the first barrier and then the second barrier and it is alternatively expelled by the second barrier and then the first barrier at a pressure determined by the input pressure against the resistance provided by the input controlled liquid and the flow control means connected between the displacement chambers. Liquids which may be used as the control liquid in the apparatus of the referenced invention as well as the present invention include water, aqueous solutions of glycols or glycerin, hydrocarbon oils, synthetic oils or the like.
In the present invention, improvements are provided in this means and method.